Wow, nice!
Taskbar is distinctly Vista-ish looking

but good. Menu is still inefficient/annoying. Like, to get to the browser you click the KDE icon, then apps, then internet, then a "web browser" section and finally you have just one icon for Konqueror.
I dont like Oxygen window decorations or widgets (except the progress bar is awesome), so I will try to use Plastik theme but with Oxygen's progress bar if I can... its strange, the Oxygen window/widgets bits look "industrial" (grey brushed metal like) but the rest of the GUI looks "MAC OSX/Vista Aqua/aero-glass like)...
Desktop crashed on me when I tried to click the settings icon (spanner)... The system notification icon remains active after you get a notification and when you click it , is says "no messages remaining" or something like that.
I'm sure they will fix the minor bugs for 4.2 final.
KDE 4.3 (next release) has plans for ARGB support for window decorations/widgets (listed in the feature plan), so expecting more Vista AERO-Glass like windows and buttons
I think when Jaunty is released in April I'll try out Kubuntu this time to see if I should switch from GNOME to KDE. But I still feel maybe KDE 4.3 will be like the actual 4.0 release not this time around with 4.2... 4.2 can be considered the actual BETA for the main KDE4 branch
Looks like KDE is leading in the beauty department (not to mention some great apps like digikam/ktorrent/k3b/amarok) while GNOME still has it's simplicity going for it... hopefully GNOME can come up with some good UI for their 3.0 release, else they will be doomed pretty soon.
I believe the QT/KDE team made the right choice for going with C++ for the GUI better than GNOME's choice for C. Probably they find more developers comfortable with C++ and easier to build UI/apps on an OO language.